It has been a while since I last discussed Coraid, but two announcements the company made at LinuxWorld earlier this month have me thinking about AoE (ATA over Ethernet) these days.

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To refresh your memory, AoE is an open source, reliable SAN transport protocol that uses MAC addresses to connect servers to their storage.

One of the knocks against AoE is that it is not routable. You can have as many arrays and disk drives as needed, but those machines and their application servers must live within broadcast reach. If this limitation is unacceptable for your requirements, you can use IP tunneling or other tools to cross those boundaries, or you can move to another protocol such as FC or iSCSI.

Another significant delimiter: AoE doesn’t support SCSI or FC drives, which means that to compensate for the SATA performance gap you must use more drives. Even so, at a cost of around $0.70 or less per gigabyte, according to Coraid, you could still get the same performance and come out ahead.

Deploying AoE in a recent version of Linux should be a breeze. According to Coraid, the kernel, from 2.6.11 on, already includes the proper drivers. Moreover, your distro, like this Ubuntu 7.04, should include the tools to discover and manage AoE storage arrays.

If your server farm includes more than just Linux machines, AoE now has drivers for Mac OS X, Windows, and Solaris, but you may have to pay a licensing fee for the first two. By installing Vblade, however, a Linux application that emulates an AoE target, you can kick the tires of AoE storage for free.

Chief among the numerous novelties Coraid CEO James Kemp mentioned in a recent conversation about AoE is an open source driver for Windows, which was developed as part of the EtherBoot Project and should become available shortly. Also worth noting is that Taiwan-based Welland has deployed the protocol in its own chips, which it will use in a SAN box for SMBs.

As for Coraid, the company announced two new appliances at LinuxWorld: the 3U, 16-drive SR1661 and the 4U, 24-drive SR2461. The SR stands for SATA plus RAID.

Both units mount SATA drives, up to the largest 1TB model. But their appeal is more than just the capacity they deliver, as the boxes also transfer data as fast as 500MBps, according to Coraid; a remarkable speed favored by the built-in 10GbE connection. Expect to pay for that speed, to the tune of $9,000 for the SR1661 and $11,000 for the 24-drive model, which should ship next month. Drives are not included in those figures.

The other announcement Coraid made at Linux world -- the EtherDrive VS21 VirtualStorage Appliance -- is among the more interesting appliances the company has unveiled in recent history, as it moves the virtualization of AoE storage to the network.

In fact, the VS21 includes its own Logical Volume Manager -- a departure from using the servers’ -- and can create as many as 255 logical volumes from Coraid storage arrays.

If other products such as the SVC (SAN Volume Controller) from IBM come to mind, you are on the right track, although the two solutions have great differences -- the transport protocol, for one.

Regardless, the VS21 brings to a Coraid SAN not only OS- and server-independent provisioning but also reliability features, including mirroring, snapshots, and serverless volume copy. You can add the VS21 to retrofit an existing Coraid installation, and adding two makes active/passive fail-over possible. Expect to pay $3,000 for each appliance, which makes the VS21 one of the more affordable steps toward virtualization.